Regioselective chemisorption-induced separate deposition of two types of metal nanoparticles on TiO2.

The discovery of the excellent thermal catalytic activity of Au nanoparticles (NPs) for CO oxidation (Haruta et al., 1987 [1]) triggered intensive research on thermal and visible photo-catalysis based on these NPs (Ref. [2]). Recently, catalysts containing two types of metal NPs loaded onto a TiO2 support, i.e., NPs consisting of a separate Au photocatalyst (average size: 13 nm) and another noble metal, were developed as highly efficient visible photocatalysts for several important chemical reactions (Tanaka et al., 2013 [3]). Although the visible photocatalytic activities of Au NPs increase as their particle size decreases (Teranishi et al., 2016 [4]), small Au NPs with a narrow size distribution could not be deposited previously because these NPs underwent dissolution and redeposition (Tanaka et al., 2013 [3]). Additionally, little is known about the mechanism of separate deposition. Herein we report a new method involving the chemisorption and subsequent NaBH4 reduction of Au(III) complex ions on TiO2-Pt. Our method enables the deposition of small Au NPs with a narrow size distribution (average size: 2.5 nm) on the TiO2 surface in TiO2-Pt (Au/TiO2-Pt). The separate deposition was rationalized in terms of the regioselective chemisorption of Au(III) complex ions on the surface of TiO2 by measuring the Au(III) complex ion adsorption. •The chemisorption and subsequent NaBH4 reduction of Au(III) complex ions on TiO2-Pt led to the deposition of small Au NPs with a narrow size distribution on the TiO2 surface of TiO2-Pt. These NPs differ from those obtained by using the existing CPH method, which produced Au NPs with a large particle size and a wide size distribution.•The separate deposition was rationalized in terms of the regioselective chemisorption of Au(III) complex ions on the TiO2 surface, although the mechanism of the CPH method was not disclosed.•Further application of the regioselective chemisorption-induced separate deposition may enable the development of new catalysts.

Dependence of crystal size on the catalytic performance of a porous coordination polymer.

Submicrosized MOF-76(Yb) exhibits a higher catalytic performance for esterification than microsized MOF-76(Yb). Control of the crystal size of porous heterogeneous catalysts, such as PCP/MOFs, offers a promising approach to fabricating high-performance catalysts based on accessibility to the internal catalytic sites.

Rational design and applications of highly efficient reaction systems photocatalyzed by noble metal nanoparticle-loaded titanium(IV) dioxide.

The fundamentals and applications of TiO(2) photocatalysis have been extensively studied in recent decades, the central theme being increasing reaction efficiency. A guideline for achieving so-called "reasonable delivery photocatalytic reaction systems (RDPRSs)" has been presented. This tutorial review summarizes recent developments in the RDPRS-based design of highly efficient photocatalytic reactions by noble metal nanoparticle-loaded TiO(2) (M/TiO(2)). After introducing the conditions required for RDPRSs, the key factors affecting the photocatalytic activity, including Fermi energy in the photostationary state, the metal particle size effect, and solvent effects are discussed. We then describe selected applications of RDPRSs for the conversion of light energy to chemical energy, environmental purification, and low-temperature cleaning of sulfur-poisoned metal catalysts. Future applications of this idea to visible-light photocatalysts, which are currently the subject of intensive research, may lead to feasible green and efficient photocatalytic reaction systems using sunlight as an energy source.

Au nanoparticle electrocatalysis in a photoelectrochemical solar cell using CdS quantum dot-sensitized TiO2 photoelectrodes.

A significant Au particle size-dependent electrocatalytic effect has been shown in a sandwich type photoelectrochemical solar cell consisting of CdS quantum dot (QD)-sensitized TiO(2) photoelectrodes, Au nanoparticle (NP)-loaded SnO(2) counter electrodes, and a polysulfide electrolyte solution intervening between the electrodes.

Size-dependence of Fermi energy of gold nanoparticles loaded on titanium(iv) dioxide at photostationary state.

TiO(2) particle-supported Au nanoparticles (NPs) with varying sizes and good contact (Au/TiO(2)) were prepared under a constant loading amount by the deposition-precipitation method. The Fermi energy of Au NPs loaded on TiO(2) at the photostationary state (E(F)') was determined in water by the use of S/S(2-) having specific interaction with Au as a redox probe. The E(F)' value goes up as the mean size of Au NPs (d) increases at 3.0

All-solid-state Z-scheme in CdS-Au-TiO2 three-component nanojunction system.

Natural photosynthesis, which achieves efficient solar energy conversion through the combined actions of many types of molecules ingeniously arranged in a nanospace, highlights the importance of a technique for site-selective coupling of different materials to realize artificial high-efficiency devices. In view of increasingly serious energy and environmental problems, semiconductor-based artificial photosynthetic systems consisting of isolated photochemical system 1 (PS1), PS2 and the electron-transfer system have recently been developed. However, the direct coupling of the components is crucial for retarding back reactions to increase the reaction efficiency. Here, we report a simple technique for forming an anisotropic CdS-Au-TiO2 nanojunction, in which PS1(CdS), PS2(TiO2) and the electron-transfer system (Au) are spatially fixed. This three-component system exhibits a high photocatalytic activity, far exceeding those of the single- and two-component systems, as a result of vectorial electron transfer driven by the two-step excitation of TiO2 and CdS.

Ultrafast photosynthetic reduction of elemental sulfur by Au nanoparticle-loaded TiO2.

Nanometer-sized gold particles with varying mean size from 3.2 to 12.2 nm were loaded on the surfaces of TiO2 particles in a highly dispersed state with the loading amount maintained constant (0.46 +/- 0.02 mass %) using the deposition-precipitation method. Light irradiation (lambda(ex) > 300 nm) to a deaerated ethanol TiO2 particle suspension containing elemental sulfur (S8) led to the energetically uphill reduction of S8 to H2S. It has been found that this reaction is dramatically enhanced with such a low level of Au loading on TiO2 and that the zero-order rate constant of reaction increases with decreasing mean size of Au nanoparticles (d). The effects of reaction parameters (substrate concentration, light intensity, temperature) on the rate of reaction were studied to infer the essential reaction mechanism. Further, a kinetic analysis has led to a conclusion that the increase in the rate of reaction with decreasing d results from the improvement of the charge separation efficiency.

Photoinduced dissolution and redeposition of Au nanoparticles supported on TiO2.

Au particles (mean size ca. 3 nm) supported on TiO(2) particles were irradiated by UV light (>300 nm) in aqueous solutions at 278 K. Photo-induced dissolution of Au nanoparticles followed by redeposition occurred in aqueous solutions containing halogen ions. The dissolution of Au nanoparticles yielded a Au(III) complex with a halogen ion; subsequent reduction of the Au(III) complex caused precipitation of larger Au particles on TiO(2).